What is a decoder and 2 to 4 DECODER
- 2. BINARY DECODERS • A binary decoder is a multi-input, multi-output combinational circuit that converts a binary code of n input lines into a one out of 2n output code.These are used when there is need to activate exactly one of 2n output based on an n-bit input value. • The figure below shows the general structure of binary decoder in which encoded information is accepted at n input lines and the output is produced at 2n possible output lines.
- 3. 2 to 4 BINARY DECODER
- 4. • The figure below shows the truth table for a 2-to-4 decoder. For a given input, the outputsY0 throughY3 are active high if enable input EN is active high (EN = 1).When both inputs A and B are low (or A= B= 0), the outputY0 will be active or High and all other outputs will be low.
- 5. • From the above truth table we can obtain Boolean expression for the each output as • These expressions can be implemented by using basic logic gates.Thus, the logic circuit design of the 2-to-4 line decoder is given below which is implemented by using NOT and AND gates.Two NOT gates or inverters provide the complement of inputs. • A common enable line is connected to eachAND gate such that when EN= 0 all the outputs are zero and if EN=1, depends on the inputs A and B, outputs are produced. Each output represents one of the minterms of the 2 input variables.
- 8. • It is also possible to design 2-to-4 decoder using NAND gates as shown in figure below along with truth table.This is constructed with a principle of max terms as outputs.To generate the minterms, we have to use NAND gates which act as inverters. If both inputs are zero (A = B = 0),Y0 will be zero , if A = 0 and B= 1, thenY1 will be 1 and so on. • Therefore, only one output will be low for any combinations of inputs at a given time and all other outputs will be high.This type of decoders is available in IC forms so that 3 to 8, 4 to 16, and 5 to 32 decoders can also be made depends on the application requirement.